(735h) Stability and Activity of IrO2-Based Homogeneous, Heterogeneous, and Hybrid Water Oxidation Catalysts

Electrochemical production of hydrogen gas is a promising energy storage technology but is limited by the slow kinetics of the oxygen evolution reaction (OER). Homogeneous and heterogenous Ir and Ru based water oxidation catalysts (WOCs) have been the most effective at catalyzing OER [1]; however, both of these elements face scarcity, cost, and stability issues [1]. One proposed method for improving the use of these precious metals is anchoring the homogeneous catalyst onto a solid support surface, via a linker molecule, to create a hybrid or immobilized catalyst that could have the benefits of both homogeneous and heterogeneous catalysts [2]. Here, we present a comprehensive computational study of the stability and activity of hybrid Ir-based WOCs and compare them to the corresponding homogeneous and heterogeneous catalysts. We show that in the presence of an IrO₂ or TiO₂ surface, all investigated homogeneous molecular species are predicted to anchor to the heterogeneous surface. For homogeneous and hybrid dimer and infinite chains, a cross-over from the WNA to the I2M mechanism, labeled as WNA-2, was observed (Figure 1). Additionally, we find that catalysts anchored on the TiO₂ surface have lower overpotential than when anchored on the IrO₂ surface; however, they exhibit a lower stability, indicating a trade-off relation between activity and stability. Finally, by doping the less stable, yet more active TiO₂ surface with Ir, the previously observed trade-off can be bridged. This work in hybrid catalysts will serve as a link between the heterogeneous and homogeneous catalyst communities and understanding the chemistry behind these mechanisms can further the development of efficient and stable WOCs.

References

1. Seitz, L. C., Dickens, C. F., et al. Science, 353(6303), 1011 LP – 1014 (2016).
2. García-Melchor, M., Vilella, L., López, N. and Vojvodic, A. ChemCatChem 8, 1792–1798 (2016).